Civil Wi-Fi projects for urban rail transit systems aim to benefit citizens by using IT to meet needs and ensure security. The launch of Wi-Fi networks throughout a metro system benefits citizens, but deployment is complex.

The first difficulty is ensuring bandwidth. To attract passengers to use a metro WLAN network, bandwidth for a single user must be the same as or better than 3G. The metro WLAN system provides 0.5-1 Mbps Internet access bandwidth for each metro passenger to browse multimedia content. Based on the train model and passenger capacity in China as well as the Wi-Fi capacity model, the train-to-ground bandwidth should be at least 400 Mbps.

The second difficulty is ensuring speed. Today's trains generally move at 120 km/hour. The services provided by the rail transit system are growing in type and quantity. Vehicle-mounted wireless APs need to frequently hand over between different trackside APs. Handover delay, packet loss rate, train-to-ground bandwidth stability are key factors that affect the metro service system in the train-to-ground link transmission. The Wi-Fi system can only provide high-quality, reliable, and uninterrupted real-time information interaction for users at metro stations and in trains when these factors are guaranteed.

The third difficulty is high-concurrency authentication. In the metro environment of a large city, the number of prospective concurrent Internet users can reach about 1 million. Implementing concurrent Internet access authentication and security control for millions of users and guaranteeing high-quality application experience are another design key and challenge.

To overcome the three major difficulties above and guarantee the network service experience of passengers anytime anywhere, it is necessary to resolve the handover problems that occur in high-speed moving of trains as well as the roaming problems of concurrent millions of online users.

Ruijie innovative patented technology: fast roaming handover within a few milliseconds

As a leading brand in data communication solutions in the industry, Ruijie adopts the 802.11ac technology to meet the high-performance train-to-ground bandwidth requirements. In the solution, Ruijie uses its patented fast roaming handover technology to achieve fast train-to-ground handover within a few milliseconds and ensure almost zero data packet loss during the handover.

The trackside APs of the entire network are considered as one big virtual AP and are coordinated by the AC in a unified manner. Vehicle-mounted APs only communicate with the big virtual AP when the train is moving and do not perceive roaming. The AC completes the train-to-ground roaming handover based on the quality of the packets received by multiple trackside APs. A series of patented technologies are used to optimize handover efficiency. Therefore, handover overhead and network packet loss will not be incurred in the roaming handover process, which greatly improves train-to-ground bandwidth and stability, and ensures smooth Internet access for passengers on the train.

In response to deployment and maintenance difficulties of trackside APs, Ruijie analyzed frequently used device deployment modes and designed the first all-in-one trackside APs in the industry. All devices used in the rail transit system comply with standards. They can work from -40°C to +70°C at 5% to 95% humidity. They are also easy to deploy and manage.

Split-type Device Used in Tunnels and Ruijie All-in-one Trackside AP

Split-type Device Used in Tunnels and Ruijie All-in-one Trackside AP

AP Deployment Inside Tunnels

AP Deployment Inside Tunnels

Ruijie innovative patented technology: "super LAN" supporting millions of concurrent users

In the metro environment of a large city, the number of prospective concurrent Internet users can reach about 1 million. To achieve the centralized authentication and management of passengers who access the Internet and to allow roaming on the Wi-Fi network in the metro environment, Ruijie has designed the whole network as an ultra-large Layer-2 LAN, using a slew of innovative patented technologies to resolve technical problems.

Ruijie's MMIS solution enhances the security of the existing metro system and enriches and extends the passenger experience. The stable ultra-high train-to-ground bandwidth greatly increases passenger viscosity. Multiple patented technologies developed in-house by Ruijie based on data from the communications industry ensure that metro Wi-Fi users do not disconnect from the network or need re-authentication, thereby greatly enhancing the passenger experience.